1. Technical Field
This disclosure relates generally to an electric rotating machine which is equipped with an outer stator, an inner stator, and a rotor disposed between the outer and inner stators.
2. Background Art
Japanese Patent First Publication No. 2013-090531, assigned to the same assignee as that of this application, teaches an example of techniques for a double-stator electric motor which is equipped with stators mounted inside and outside a rotor in a radial direction thereof in order to improve the output performance thereof. The double-stator electric motor includes an inner stator core and an outer stator core which have axial ends jointed together by a retainer plate through welding.
The retainer plate is supported only by the axial ends of the inner and outer stator cores, thus resulting in a difficulty in achieving alignment of the centers of the stator cores with the axis of rotation thereof or setting a positional relation between the inner and outer stator cores in a circumferential direction thereof, which may lead to misalignment between the inner and outer stator cores. For instance, misalignment between the inner and outer stator cores in the radial direction thereof results in formation of a non-uniform gap between the stator and the rotor, which produces magnetic vibration. The misalignment between the inner and outer stator cores in the circumferential direction thereof results in overlap in peak between inner and outer electromagnetic powers, which may lead to an increase in the torque ripple.
The above structure also encounters the drawback in that the retainer plate is easy to flex or deform, thus causing the stator cores to be shifted from the correct position. This may result in magnetic vibration or an increase in torque ripple, as described above, which, in the worst case, leads to a physical contact between the stators and the rotor, so that they are damaged. The axial misalignment between the rotor and the stators may result in a decrease in effective region through which the magnetic flux flows, so that the output torque drops or a thrust force is created to cause mechanical vibration.